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TWICE DAILY ASPIRIN MAY BE BETTER FOR DIABETICS

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Twice-daily aspirin administration, but not a once-daily doubling of the dose, appears to provide good inhibition of platelet cyclooxygenase (COX)-1 in diabetic patients who have rapid recovery of COX-1 activity and might enhance cardiovascular protection, Francesco Zaccardi, MD, a diabetology fellow at Catholic University of Sacred Heart in Rome, Italy, reported here at the European Association for the Study of Diabetes (EASD) 47th Annual Meeting.
Aspirin is currently recommended for cardiovascular protection for patients with type 2 diabetes mellitus, regardless of prior vascular events. But primary prevention trials have failed to demonstrate its efficacy in this population, possibly because of incomplete platelet inhibition. Italian researchers, led by Dr. Zaccardi, investigated glycemic control and other factors as possible reasons for the incomplete inhibition of thromboxane A2 by low-dose aspirin over 24 hours. Thromboxane A2, a product of COX-1 activity, is prothrombotic.
The investigators recruited 100 patients with type 2 diabetes who were taking 100 mg of aspirin daily. They measured thromboxane B2, the hydrolysis product of thromboxane A2 and a marker of platelet COX-1 activity, every 3 hours, between 12 and 24 hours after an observed aspirin administration, to assess the kinetics of recovery of COX-1 activity. In addition, a subset of 46 patients underwent 24-hour continuous glucose monitoring. Of them, the 33 patients with the steepest slopes of recovery of COX-1 activity were randomly assigned to receive aspirin 100 mg daily (n = 11), 200 mg daily (n = 11), or 100 mg twice daily for 28 days (n = 11). Recovery of COX-1 activity was determined on day 29 during the 12- to 24-hour dosing period.
The researchers found that COX-1 activity showed linear kinetics with large variability among individuals in the slope of recovery of enzyme activity. For the patients in the lowest tertile of recovery of activity, serum thromboxane B2 increased in the 12- to 24-hour period by 0.02 ng/mL per hour (range, 0.01 to 0.03 ng/mL per hour), compared with an increase of 0.14 ng/mL per hour (range, 0.11 to 0.20 ng/mL per hour) for the tertile with the fastest recovery.
Independent predictors of the slope of thromboxane B2 recovery were mean platelet volume (MPV) (P < .0001), higher body mass index (BMI) (P = .007), and age (P = .049). None of the parameters studied in continuous glucose monitoring (e.g., mean 24-hour glycemic value, mean amplitude of glycemic excursions), nor glycated hemoglobin or fasting glucose level, predicted the slope of recovery of thromboxane B2.
In the cohort with the steepest slopes of return of COX-1 activity, the subjects taking 100 mg of aspirin twice daily showed complete normalization of the slope of platelet COX-1 activity; the administration of 200 mg daily did not have such an effect. Compared with 100 mg once daily, the once-daily administration of 200 mg of aspirin reduced the slope of the recovery line by 55%, and 100 mg of aspirin twice daily reduced the slope by 88% (P < .05 for each vs 100 mg once daily).
Considering the predictive effect of MPV, Dr. Zaccardi surmised that the interindividual variability in the return of COX-1 activity probably reflects abnormal megakaryopoiesis associated with type 2 diabetes. Furthermore, BMI might affect the pharmacokinetics after aspirin dosing. He concluded that twice-daily aspirin administration can overcome the inadequate thromboxane B2 inhibition seen with once-daily dosing. He advised performing larger, randomized clinical trials to test the safety and effectiveness of this approach.
Since it is not feasible to measure COX-1 activity or thromboxane B2 in routine clinical practice, Dr. Zaccardi told Medscape Medical News that in the future, we will likely "have to focus more attention on BMI, on age, and on MPV, because it's very easy to measure BMI and to obtain the value of MPV from a single blood analysis."
In summary, he said that an important finding of the study is that "one third of type 2 diabetic patients are poor responders to aspirin, and probably they need twice-daily administration of aspirin." He speculated that the one third of patients who are poor responders to aspirin might have diluted out an effect in the other two thirds in primary prevention trials, possibly accounting for the failure of those trials to show efficacy.
With twice-daily dosing, compliance could be a problem. A slow-release formulation of 200 mg of aspirin could be helpful, but does not now exist, Dr. Zaccardi said. Session cochair Michael Cummings, MD, professor of diabetes and endocrinology in Portsmouth, United Kingdom, said he doubts that adding 1 more pill a day for an elderly type 2 diabetic patient on multiple medications already would present much of an additional problem.
He noted that guidelines in the United States and in Europe focus on using once-daily aspirin, so the study is intriguing for its use of twice-daily dosing, which has not been studied previously. "The implications of the study could be that a simple change to the way that we dose aspirin at the moment — [twice-daily] dosing — could lead to different clinical outcomes, and could perhaps have more pronounced cardiovascular benefits than we're seeing with once-daily aspirin," he said, "particularly in patients with type 2 diabetes."
Dr. Cummings noted that it is becoming increasingly apparent that how and when drugs are administered can change outcomes. As an example, he cited recent work showing that nighttime dosing of antihypertension drugs is probably better than taking them in the morning.
Dr. Cummings advised that future trials of aspirin in people with type 2 diabetes will need to look at cardiovascular outcomes, not just mechanisms of platelet inhibition. Dr. Zaccardi agreed, and said that in light of current good regimens for glycemic, cholesterol, and blood pressure control, "what we have to improve is the problem of [platelet] aggregation in diabetic patients. It is probable that this study could represent a solution...[to] the reduced ability of aspirin to block COX-1."

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